A multi-faceted chemical and physical approach is proposed to determine, by direct measurement, the extent of helical secondary structure in undegraded rabbit globin and silk-moth chorion protein messenger RNAs. The 3'hydroxyl polyadenylic acid sequences, normally present in these mRNAs, will be enzymatically removed. Studies of the deadenylated mRNAs will be undertaken to detect possible changes in secondary structure compared to the intact molecules. Rabbit alpha and beta globin mRNAs will be subjected to controlled hydrolysis, and 3'hydroxyl fragments containing 50-60 nucleotides in addition to the poly(A) sequences will be isolated. These fragments will be studied to search for helical regions predicted by existing nucleotide sequence data. Radioactive carbodiimide compounds are used as covalent probes to estimate the number of reactive nucleotides in non-helical regions. The base composition and thermal stability of helical regions will be estimated by absorbance and circular dichroism measurements. Single- strand specific nuclease digestion and analysis of products on polyacrylamide-formamide gels will provide data on the nucleotide length of double-stranded regions. Ethidium bromide binding to double helical regions will be studied by absorbance and fluorometric techniques. The proposed research program will yield information basic to future detailed considerations of the relationship of the secondary structure of eucaryotic messenger RNA to it's biological function and stability. Results obtained will be interpreted to suggest models for the in-solution structure of mRNA.